One of the factors that define the complexity degree of a finned casing of a rotating electrical machine is the height per distance ratio between the fins; such ratio affects the casting process and the finishing process of the finished product, especially in painting. An optimization of the fins aiming at maximizing the convection coefficient may result in a minimization of this ratio without compromising the heat exchange in most part of the casing surface. However, it is unavoidable that along the casing height the convection coefficient is reduced, especially in the front region, once the air flowing speed intensity experiences reduction in function of the distance run and of the respective spacing regarding ventilation system basically due to intrinsic losses to the air flowing displacing process. In turn, the convection coefficient is directly correlated with the air speed and the heat exchange area.